For the filtering out of fibers from a stream of air from textile machinery, the stream is conducted through a filter which retains the fibers borne in the air stream. This fibrous material builds up firmly on the filter and thus reduces the capacity for low pressure, which reacts through a piping system at different places on the machine in order to carry away free floating, undesirable fibers. In order to assure the functional ability of the low pressure system, from time to time the filter is cleaned by means of a scraper blade. In accord with a known process (DE 44 27 771 A1) for this purpose, a vertical scraper blade is run in a horizontal direction over the filter, and is subsequently lifted from the filter and returned to its original position. In order to execute this process, a complicated apparatus is necessary in order to impart to the scraper blade the desired movements. Moreover, fibrous material can agglomerate on the scraper blade, thereby reducing the efficiency of the same.